Mosquitoes ignore repellent

Scientists have questioned the impact a widely-used insect repellent is having against mosquitos.

Researchers from the London School of Hygiene say that in their tests mosquitoes were initially deterred by Deet but after awhile they began to ignore it.

They have suggested that alternatives need to be found for Deet after they conducted a test on its effectiveness on the Aedes aegypti species of mosquito that spreads dengue and yellow fever.

It is suspected that insects simply do not like the smell of Deet, a widely used ingredient in repellents developed by the US military, but it seems mosquitoes are now beginning to ignore it.

Dr James Logan from the London School of Hygiene and Tropical Medicine, said: “The more we can understand about how repellents work and how mosquitoes detect them, the better we can work out ways to get around the problem when they do become resistant to repellents.”

He said that during the tests his team recorded the response of the receptors on the antenna of the mosquitos to Deet and after a while found they were no longer as sensitive to the chemical.

“There is something about being exposed to the chemical that first time that changes their olfactory system - changes their sense of smell - and their ability to smell Deet, which makes it less effective,” he added.

Dr Logan said that mosquitos had shown they were good at evolving very quickly.